This invention relates to a new technique for improving the electrical characteristics, particularly the voltage regulation properties of batteries, e.g., the Li/FeS.sub.2 thermal battery.
In many galvanic systems, a variety of voltage irregularities is known to occur. These include voltage transients or voltage "spikes" during initial discharge or at other times, plateaus during discharge, inconsistencies during discharge, particularly near the end of useful discharge life, lot to lot irreproducibility, intra-lot irreproducibility, etc. There has long been a need to eliminate or ameliorate these difficulties.
In the very common lithium/iron disulfide battery, such voltage irregularities are particularly bothersome. These batteries essentially comprise a lithium metalcontaining anode (negative electrode) and an iron disulfide-containing cathode (positive electrode). Some operate at ambient (room) temperature or intermediate temperatures (approximately 150.degree. C.) and utilize a liquid non-aqueous electrolyte. Others operate at very high temperatures (e.g., greater than 300.degree. C.) and utilize a molten salt electrolyte (thermally activated batteries). The latter usually employ a higher melting lithium alloy for the negative electrode rather than pure lithium, e.g., Li(Al) or Li(Si). In addition to the solid anode and cathode components, such batteries also include heat pellets which are ignitable thereby supplying sufficient heat to render the electrolyte molten and to initiate the discharge of the battery.
Both forms of the battery are well known. For example, U.S. Pat. Nos. 4,172,926, 4,164,069, 3,992,222, 4,223,078 and 4,084,045 deal with prior art rechargeable (secondary) or ambient temperature batteries of the Li/Fe/S system. U.S. Pat. No. 4,383,014 is typical of prior art attempts at improving the voltage inconsistencies existing in known thermal batteries. It attempts to eliminate the bothersome initial voltage transient ("spike") by inclusion in the cathode composition of an empirically found additive (CaSi.sub.2) theorized to produce local short-circuiting (depolarization) immediately after initiation of the battery. However, this and other attempted solutions have been entirely unsatisfactory.
There remains a serious need for improvements in the voltage regulation of batteries, e.g., thermal batteries, e.g., including amelioration or elimination of voltage transients, voltage fall-offs, plateauing effects, and other voltage irregularities as well as a lengthening of useful discharge lifetimes, and improvements in reproducibility as mentioned above.